Image: Testing the electrical power subsystem of NASA's James Webb Space Telescope
The spacecraft bus will provide the necessary support functions for the operation of the Webb Observatory after it is launched into space in 2018.
The bus is the home for six major subsystems:
- Electrical Power Subsystem
- Attitude Control Subsystem
- Communication Subsystem
- Command and Data Handling Subsystem
- Propulsion Subsystem
- Thermal Control Subsystem
The Electrical Power Subsystem or EPS provides the power needed to operate the whole observatory. The EPS converts sunlight shining on the solar array panels into the power needed to operate the other subsystems in the bus as well as the Science Instrument Payload.
The Attitude Control Subsystem senses the orientation of the Observatory, maintains the Observatory in a stable orbit, and provides the coarse pointing of the Observatory to the area in the sky that the Science Instruments want to observe.
The Communication Subsystem is the ears and mouth for the Observatory. The system receives instructions (commands) from the Operations Control Center and sends (transmits) the science and status data to the OCC.
The Command and Data Handling (C&DH) System is the brain of the spacecraft bus. The system has a computer, the Command Telemetry Processor (CTP) that receives commands from the Communications System and directs them to the appropriate recipient. The C&DH also has the memory/data storage device for the Observatory, the Solid State Recorder (SSR). The CTP will control the interaction between the Science Instruments, the SSR and the Communications System
The Propulsion System contains the fuel tanks and the rockets that, when directed by the Attitude Control System, are fired to maintain orbit.
The Thermal Control Subsystem maintains the operating temperature of the spacecraft bus.